报告题目：Dirac-fermion approach and its application to layered magnetic topological insulators

报告人：张海军，南京大学教授

报告时间：2023年7月5日  9：00

报告地点：伟德BETVlCTOR1946中心校区唐敖庆楼B521

报告人简介

张海军，南京大学教授，长期从事计算凝聚态物理方面的前沿基础研究，探索和理解凝聚态物理中的各种新奇物性，特别在拓扑量子材料探索和拓扑物性研究方面取得了一些具有国际影响力的原创性研究成果。与合作者，发现了一系列代表性的拓扑量子材料体系（Bi₂Se₃家族拓扑绝缘体、MnBi₂Te₄家族本征磁性的轴子绝缘体，2M-WS₂二维材料拓扑超导）；原创性提出了基于最局域Wannier函数的拓扑物性数值计算方法等。目前发表SCI学术论文80余篇，论文总引用超过17500次。

报告摘要

　　The recently discovered MnBi₂Te₄-family magnetic topological insulators (TIs), have aroused great attention, where the interlayer vdW gap is expected to play a crucial role in topological surface states. Here, we develop a simple Dirac-fermion approach which is valuable to understand and design magnetic topological states in various multilayers of layered magnetic topological insulators. Based on the Dirac-fermion approach, we demonstrate how to understand and tune high Chern numbers in ferromagentic MnBi₂Te₄ films through the van der Waals (vdW) gap modulation. We also apply the Dirac-fermion approach to the surface states of vdW antiferromagnetic TIs. Remarkably, unexpected topologically protected gapless Dirac-cone surface states are found to arise under a slight surface vdW gap expansion, if the surface ferromagnetic layer has a zero Chern number, while the surface states remain gapped for all other cases. The unexpected gapless Dirac-cone states are invaluable in solving the puzzle of the observed gapless surface states in MnBi₂Te₄.

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